Apparatus and a method of determining hydrogen by use of a neutron source

ABSTRACT

This invention relates to an apparatus for the detection of the hydrogen content of an object, wherein said apparatus comprises a neutron source that emits fast/energy-rich neutrons; a detector device for detecting thermal neutrons; a moderator that brakes and reflects neutrons upon collision; wherein said detector device comprises a light-emitting unit that emits light in case of a nuclear event/reaction with a thermal neutron; a light-registering unit that emits an electric pulse/an electric signal when a flash of light is detected; and wherein said moderator is a light-conductive unit arranged between said light-emitting unit and said light-registering unit. Moreover the invention relates to a corresponding method of detecting hydrogen. Hereby an apparatus and a method are provided for the detection of humidity/water/hydrogen with improved sensitivity which entails that the used neutron source need not be as powerful and that smaller amounts of hydrogen can be detected compared to previously suggested solutions. Moreover, a reliable non-modifying/non-destructive detection is provided.

This invention relates to an apparatus for detecting the contents ofhydrogen in an object.

This invention also relates to a method of detecting the contents ofhydrogen in an object.

In general, the invention relates to a detection apparatus that is ableto detect hydrogen (for instance for detecting an amount of water) in anobject by use of a neutron source. A neutron source for this purposepresents the advantage ia that neutrons are able to penetrate certainbarriers. For instance, it is possible by this invention to estimate theamount of hydrogen, water and/or humidity in eg insulation materialarranged in ia a steel pipe. It can be used for checking whether and howmuch water/humidity there is present in the insulation material, whichis important to know eg in connection with the assessment of the risk ofcorrosion, rust, etc. This may be performed without having to remove orcut in parts of the pipe/object or to separate the object/pipe or partsthereof.

A source of fast neutrons emits fast/energy-rich neutrons, ie neutronswith high kinetic energy. In the present invention the known discoveryis used to advantage that atomic nuclei (and in particular hydrogen)brake neutrons upon collision, a phenomenon typically referred to aselastic scattering/collision (whereby the velocity is reduced and thedirection is changed for a collided neutron). This invention uses adetector device that detects relatively slow/energy-poor neutrons, theso-called thermal neutrons. After a neutron has been brakedsufficiently, it can be detected by the detector device. The process ofbraking neutrons is typically designated ‘moderation’ and a physicalarranged for this a ‘moderator’. In order for a neutron to be detected,most often is has to collide several times with hydrogen atoms.

In order to accomplished an increased sensitivity it is known toconfigure the detection apparatus to comprise an (auxiliary) moderator,an amount of hydrogen or a moderator material that brakes andreflects/scatters neutrons by elastic scattering/collision and isarranged such that a portion of incoming neutrons are reflected againstthe detector and the hydrogen for detection. In broad outline thefurther amount of hydrogen/moderator material serves as a (partial)neutron reflector that also brakes the neutrons, thereby causing alarger amount of braked/thermal neutrons to be detected. This is alsooften referred to as neutron back-scatter.

Patent specification GB A 1180450 discloses an arrangement for detectinghumidity/hydrogen by use of a neutron source. The arrangement accordingto GB A 1180450 is shown schematically in FIG. 1 and comprises afast-neutron source (103), a detector for thermal neutrons (102) and ahydrogen-containing neutron-braking and -reflecting/-scattering material(ie moderator material) (104) for providing the back-scatter effect,wherein the detector (102) and the source (103) are arranged betweenthis material (104) and the material/object (101) in which thehumidity/water/hydrogen is to be detected.

It is mentioned in patent specification GB A 1180450 that the detectorof thermal neutrons (102) may be a scintillator.

Albeit the detector according to GB A 1180450 has an increasedsensitivity due to the moderator (104), it is possible to accomplishsuperior sensitivity as taught by the present invention.

Patent specification U.S. Pat. No. 3,707,631 relates to a system fornon-destructive analysis of nuclear fuel, wherein a neutron source and adetector device are arranged to each their side of the sample. Thesource emits low-energy neutrons (<1 Mev), ie not thermal, where acomparatively large moderator brakes the emitted neutrons to the effectthat they can initiate a fission process that emits fast (>1 Mev)neutrons that are detected in an energy-selective scintillator. In thissystem, measurement is performed on fast neutrons and various measuresmust be taken to separate them from the (almost equally) fast neutronsfrom the source that have not been braked. A light guide is alsomentioned, the primary function of which is to couple a number of verydifferent scintillator geometries to the front of a standardphoto-multiplier.

The arrangement disclosed in U.S. Pat. No. 3,707,631 is not directedagainst or suitable for the detection of hydrogen.

Patent specification No. U.S. Pat. No. 5,446,288 teaches detection ofhydrogen and other light elemental substances using detection of whenthermal neutrons, where light source and detector are on the same sideof the sample. A detector device comprises a scintillator coupled to aphoto-multiplier via a light guide in the form of an air light guide,wherein the neutron source is enclosed by moderator material that isseparated from the light guide.

It is an object of the invention to provide an apparatus for thedetection of humidity/water/hydrogen and exhibiting improvedsensitivity.

It is a further object of the invention to provide a detectionapparatus, wherein the strength of the used neutron source need not beas powerful as in the prior art.

It is a further object of the invention to provide a detection apparatuswith reliable, non-modifying/non-destructive detection.

It is also an object of the invention to provide a compact detectionapparatus.

These objects are provided by an apparatus of the kind described aboveand comprising:

-   -   a neutron source that emits fast/energy-rich neutrons;    -   a detector device for detecting thermal neutrons;    -   a moderator that brakes and reflects neutrons upon collision;        wherein    -   said detector device comprises        -   a light-emitting unit that emits light in case of a nuclear            event/reaction with a thermal neutron; and        -   a light-registering unit that emits an electric pulse/an            electric signal when a flash of light is detected; and    -   said moderator is a light-conductive unit arranged between said        light-emitting unit and said light-registering unit.

Hereby a hydrogen-detector/humidity probe is achieved that featuresimproved sensitivity, the light-conductive unit providing aconductivity/concentration of the light from the light-emitting unit tothe light-registering unit, thereby further improving theperformance/sensitivity, as it is ensured that all nuclear events thatbring about a flash of light will, with a much increased degree ofreliability, be registered by the light-registering unit.

Moreover, the dual function of the light-conductive unit, as it alsoprovides a moderating effect, ie contains hydrogen/moderator materialfor accomplishing the above-mentioned back-scatter effect, means thatthe apparatus according to the invention can be configured to be compactor at least not with dimensions that exceed the solutions that alreadycomprise an auxiliary moderator.

The increased sensitivity means that the used neutron source need not beso powerful as to constitute a health risk and thus presupposes safetyequipment for an operator or cumbersome handling thereof, whilesimultaneously a reliable, non-modifying/non-destructing detection isstill provided, ie without modification of a measurement object (egsampling, cutting off a part of a pipe/object, taking it apart, etc).Moreover, smaller amounts of hydrogen can be detected compared topreviously known solutions, due to the increased sensitivity.

According to one embodiment, said light-emitting unit is a scintillatorand said light-registering unit is a photo-multiplier (PM)).

Alternatively the light-registering unit is a photo-diode.

According to one embodiment, said source is comprised of or embedded insaid moderator. Hereby a compact detector is provided.

According to a preferred embodiment said light source is arrangedessentially in proximity of or in/around the centre of the face of saidmoderator that adjoins the light-emitting unit.

This position has proved to be convenient in order to accomplishedfurther enhanced sensitivity, as a larger amount of neutrons will bereflected and moderated and hence detected.

According to one embodiment said light-conductive unit is configuredessentially with a face that adjoins said light-emitting unit and havinga relatively smaller face adjoining a detection face of saidlight-registering unit.

Hereby a comparatively larger face of the light-emitting unit can becoupled optically to a smaller detection face of the light recordingunit, which yields an advantage with regard to economics, the cost ofsuch light-registering units being relatively high and depending to alarge extent on the recording area.

For instance, said light-conductive unit may be configured essentiallyas a cone, where the top is cut way (ie a trapezoidal shape in 2D/incase of a section in the centre line of the cone as indicated eg in FIG.2 a).

In one embodiment, said light-conductive unit is configured for emittinglight conducted from said light-emitting unit to the light-registeringunit essentially perpendicular to a detection face of the apparatus.

Hereby a detection apparatus is readily provided that has a largerexpanse essentially perpendicular to a detection face of the object inwhich hydrogen is to be detected. This gives an advantageous embodiment,in particular if the detection apparatus according to the invention isintended for being operated primarily in a depth/in a longitudinaldirection.

According to an alternative embodiment said light-conductive unit isconfigured for emitting light conducted from said light-emitting unit tothe light-registering unit essentially in parallel with a detection faceof the apparatus.

In this manner a detection apparatus is readily provided that has alarger expanse, essentially in parallel with a detection face of theobject in which hydrogen is to be detected. In popular terms thedetection apparatus is longer than it is wide. Hereby an advantageousconfiguration is provided, in particular if the detection apparatusaccording to the invention is intended for being handheld and operatedmanually.

According to one embodiment the apparatus further comprises an electriccircuit connected to said detector device, wherein said circuit isconfigured for generating a signal that represents an estimated amountof hydrogen, water and/or humidity content on the basis of the electricsignal from said light-registering unit.

Moreover the invention relates to a method of detecting hydrogen contentof an object comprising the steps of:

-   -   emitting fast/energy-rich neutrons from a neutron source;    -   detecting thermal neutrons by means of a detector device;    -   braking and reflecting neutrons by collision of a moderator,        wherein the method further comprises:    -   emitting light by a light-emitting unit by a nuclear        event/reaction with a thermal neutron;    -   emitting an electric pulse/an electric signal by a        light-registering unit upon recording of a flash of light; and    -   conducting light from said light-emitting unit to said        light-registering unit by a light-conductive unit arranged        between said light-emitting unit ands said light-registering        unit; of which said moderator is the light-conductive unit.

According to one embodiment said light-emitting unit is a scintillatorand said light-registering unit is a photo-multiplier (PM) or aphoto-diode.

According to one embodiment said source is comprised of or embedded insaid moderator. Hereby compact detection is provided.

According to one embodiment said source is arranged essentially inproximity of or about/in the centre of the face of said moderator thatadjoins the light-emitting unit.

According to one embodiment, said light-conductive unit is configuredessentially with a face adjoining said light-emitting unit and having arelatively smaller face adjoining a detection face of saidlight-registering unit.

According to one embodiment said light-conductive unit is configured foremitting light conducted from said light-emitting unit to the lightregistering unit essentially perpendicular to a detection face.

According to one embodiment said light-conductive unit is configured foremitting light conducted from said light-emitting unit to thelight-registering unit essentially in parallel with a detection face.

According to one embodiment the method further comprises generationwithin an electric circuit connected to said detector unit a signalrepresenting an estimated amount of hydrogen, water and/or humiditycontent, wherein said generation is performed on the basis of theelectric signal from said light-registering unit.

The method according to the invention and embodiments thereof correspondto the apparatus according to the invention and embodiments thereof andhave the same effects for the same reasons.

In the following the invention will be explained in further detail withreference to the drawing, wherein

FIG. 1 illustrates prior art that uses the back-scatter principle fordetecting hydrogen/water;

FIG. 2 a schematically illustrates an embodiment of an apparatusaccording to the invention;

FIG. 2 b schematically illustrates an embodiment of an apparatusaccording to the invention;

FIG. 2 c schematically illustrates an alternative embodiment of anapparatus according to the invention.

FIG. 1 illustrates the prior art that uses the back-scatter principlefor detecting hydrogen/water. Shown is a detection apparatus (100) fordetecting hydrogen in an object (101). The detection apparatus (100)comprises a moderator containing hydrogen (104), a fast-neutron source(103), and a detector for thermal neutrons (102), wherein the neutronsource (103) and the detector for thermal neutrons (102) are arrangedbetween the moderator (104) and the object (101) by use of a detectionapparatus (100). Moreover a detection face (109) for the detectionapparatus (100) is shown schematically, ie the face to be arrangedadjoining the object (101) in which hydrogen is to be detected. Neutronsemitted by the source (103) will have largely all directions, and someof these neutrons will collide with the hydrogen both in the moderator(104) and with the hydrogen that is to be estimated in the object (101),whereby the neutrons will change direction and loose speed. A portion ofthe neutrons will be reflected against the detector by thermal neutrons102, and when they have collided sufficiently many times they will bethermal (ie they will typically have a kinetic energy within the rangeof about approximately 0.025 eV), whereby the detector will record them,and the amount of hydrogen in the object (101) can be detected. Someneutrons will be reflected both by the moderator (104) and the hydrogenin the object (101), while others will continue in other directionsand/or be absorbed. Typically a neutron shall collide in average sixtimes with a hydrogen atom in order to have an energy that the detectoris able to detect (the neutron needs to reduce its energy level byapproximately 6 to 8 orders of magnitude). The moderator (104) providesthe effect that more neutrons with a suitable energy will be detectedcompared to a scenario in which it was only the hydrogen in the testobject (101) that was primarily present for reducing the kinetic energyof the neutrons. Hereby the sensitivity of the detection apparatus (100)is enhanced.

FIG. 2 a schematically illustrates an embodiment of an apparatusaccording to the invention. Shown in the figure is a detection apparatus(100) that comprises a neutron source (103) and neutron-braking and-reflecting material (104′), ie moderator material, eg comprisinghydrogen. The detection apparatus (100) has a detection face (109) thatis intended for being directed towards or against an object (101) inwhich hydrogen is to be detected.

Moreover the detection apparatus (100) comprises a detector of thermalneutrons (102 a, 102 b) that comprises, in accordance with theinvention, a light-emitting unit (102 b) and a light-registering unit(102 a), wherein the light registering unit (102 a) is connected to anelectric circuit (105). The light-emitting unit (102 b) emits light by anuclear event/reaction with a thermal neutron, while thelight-registering unit (102 a) emits an electric pulse/an electricsignal (106) upon registration of a flash of light, where the emittedelectric pulse/the emitted electric signal is received in the electriccircuit (105) for subsequent interpretation, processing, etc.

According to the invention the moderator material is a light-conductiveunit or a light-conductive material (104′). In this manner thelight-conductive unit (104) comprises both a moderating effect, iecontains hydrogen/moderator material for obtaining the above-referencedback-scatter effect, and conducting/concentrating light from thelight-emitting unit (102 b) to the detection face (107) of thelight-registering unit (102 a), thereby further enhancing theperformance/sensitivity, it being ensured that all nuclear events thatbring about a flash of light will, with a much higher degree ofcertainty, be recorded by the light-registering unit (102 a), therebyenabling that smaller amounts of hydrogen can be detected without anensuing need to increase the strength of the neutron source.

The movement of the light from the light-emitting unit (102 b) to thelight-registering unit (102 a) is shown schematically by dotted arrowsin the figure.

Moreover the dual function of the light-conductive unit/moderator (104′)means that the detection apparatus (100) can be configured compact or atleast not larger than solutions that already comprise an auxiliarymoderator for achieving neutron back-scatter.

In the shown embodiment the light-conductive unit (104′) is configuredessentially with a face adjoining said light-emitting unit (102 b) andhaving a relatively smaller face adjoining a detection face (107) of thelight-registering unit (102 a).

Hereby a relatively larger face of the light-emitting unit (102 b) canbe coupled optically to a smaller detection face (107) of thelight-registering unit (102 a), which yields an advantage from afinancial point of view, as the price of such light-registering units(102 a) is comparatively high and to a large degree depend on theregistration area.

For instance, the light-conductive unit can be configured essentially asa cone, where the top is cut away (ie a trapezoidal form in 2D/in caseof a section in the centre line of the cone, eg as shown in thedrawing).

The light-conductive unit/the light-conductive material (104′) may eg bea light-guide (English term) comprising hydrogen and/or other moderatormaterial. According to a preferred embodiment the light-guiding unit/thelight conductive material (104′) comprises Plexiglas.

Preferably the neutron source is comprised of/embedded in said moderator(104′) and arranged essentially around or in the centre of the face ofsaid moderator (104′) that adjoins the light-emitting unit (102 b).

This arrangement has proven to be convenient in order to obtain enhancedsensitivity as a larger number of neutrons will be reflected andmoderated and hence detected.

According to one embodiment the light-emitting unit (102 a) is ascintillator, which is a known standard unit that records a nuclearevent and emits a flash of light when eg a thermal neutron hits thescintillator (102 b). In practice photons are released. One example of ascintillator (102 b) includes glass enriched with the lithium isotopeLi-6.

According to one embodiment the light-emitting unit (102 b) is aphoto-multiplier, which is also a known standard unit that records evenvery weak flashes of light/photons and generates an electric pulse onthe background of one or more of such. Alternatively thelight-registering unit (102 a) is a photo-diode.

The electric circuit (105) receives electric pulses/signals from thelight-registering unit/photo-multiplier (102 a) and is thus able torecord and/or process these signals depending on the relevant use, egfor estimating the amount of water/humidity/hydrogen in the object (101)or for other applications. For instance, one or more electric outputsignals (108) from the electric circuit (105) can be used eg for adisplay/meter (not shown) that shows the estimated amount and/or otherfunctions.

Moreover the detection apparatus (100) may comprise other types(optionally non-hydrogen-containing materials) of light-conductivematerial (104′) as long as they have a neutron-moderating effect.

Preferably the light-registering unit/photo-multiplier (102 a) and thelight guide (104) will collide/adjoin each other at the detection face(107) of the light-registering unit/the photo-multiplier with an opticaladaptor material there between, such as eg silicon grease, transparentsilicon, joint filler, etc. to ensure as low an optic loss as possibleby the transition.

The neutron source (103) may be eg an isotope-based neutron source.

Alternatively the neutron source (103) can also be arranged elsewherethan within/around the centre of the light guide (104′).

The electric circuit (105) may have many functions and configurationsdepending on the current use of the invention. A simple electric circuitmerely has to record the number of electric pulses from thephoto-multiplier/the light-registering unit (102 a) for a period of timein order to be able to estimate the amount of water/hydrogen in a simplemanner. Alternatively more sophisticated electric circuits can be used.

Moreover the apparatus (100) may comprise a material disc, plate, piece,etc (not shown) arranged such that the neutron source (103) is betweenthat and the detection face (109). Said disc, plate, piece, etc, must beof a material that possesses the property that it is good at reflectingneutrons without considerable loss of energy, eg iron or molybdenum.Moreover the apparatus (100) may comprise a ring, pipe, cylinder, etc,arranged such that it encircles the neutron source (103), whereby gammaradiation, if any, is removed that may otherwise give false hits uponreaction with the light-emitting unit (102 b). This ring, pipe,cylinder, etc, has to be of a material that possesses the property that,to a particular extent, it absorbs gamma radiation, eg lead or wolfram.

FIG. 2 b schematically illustrates an alternative embodiment of anapparatus according to the invention. Shown in the figure is a detectionapparatus (100) according to the invention comprising the sameelements/units as shown in and explained in connection with FIG. 2 a,but wherein they are arranged and optionally configured differently.More specifically the combined moderator and light-conductive unit(104″) is configured such that it essentially conducts the light inparallel with the detection face (109) of the detection apparatus (100)to the light-registering unit (102 a) (conversely to the embodimentshown in FIG. 2 a, where the light is conducted essentiallyperpendicular to the detection face (109), thereby enabling a ratherelongate configuration of the detection apparatus (100). Thelight-conductive unit (104″) may be configured eg as shown in thefigure, with a 2D profile as a triangle, wherein the incoming light fromthe light-emitting unit (102 b) is reflected essentially perpendicularin relation to the incoming direction, ie essentially in parallel withthe detection face (109).

Alternatively the light-conductive unit (104″) may be a batch of opticalfibres/optical fibre cable that angles/turns/deflects the light sidewaysin relation to the primary angle of incidence, ie essentially inparallel with the detection face (109).

The movement of the light from the light-emitting unit (102 b) to thelight-registering unit (102 a) is shown schematically by dotted arrowsin the figure.

In the shown embodiment, the light-conductive unit (104″) is configuredessentially with a face adjoining said light-emitting unit (102 b) andhaving a relatively smaller face adjoining a detection face (107) of thelight-registering unit (102 a).

The elongate configuration is particularly useful if the detectionapparatus (100) is to have a configuration that is suitable forhandheld/manual operation with ensuing easier handling/operation.

FIG. 2 c schematically illustrates an alternative embodiment of anapparatus according to the invention. The shown embodiment correspondsto the one shown in FIG. 2 a, but wherein the location of the neutronsource (103) is changed. In the shown embodiment the neutron source(103) is arranged more towards the centre of the moderator (104′), ienot in the face of the moderator (104″) that adjoins the light-emittingunit (102 b). Alternatively, the neutron source (103) can be arranged egmore towards the sides of the moderator (104′). The same modification ofthe position of the neutron source can also be performed in theembodiment shown in FIG. 2 b or others.

1. An apparatus for detecting the hydrogen content of an object (101),wherein the apparatus (100) comprises a neutron source (103) that emitsfast/energy-rich neutrons; a detector device (102; 102 a; 102 b) fordetecting thermal neutrons; a moderator (104; 104′; 104″) that brakesand reflects neutrons upon collision; characterised in that saiddetector device comprises a light-emitting unit (102 b) that emits lightin case of a nuclear event/reaction with a thermal neutron; and alight-registering unit (102 a) that emits an electric pulse/an electricsignal (106) when a flash of light is detected; and that said moderator(104′, 104″) is a light-conductive unit arranged between saidlight-emitting unit (102) and said light-registering unit (102 a).
 2. Anapparatus according to claim 1, characterised in that saidlight-emitting unit (102 b) is a scintillator and that saidlight-registering unit (102 a) is a photo-multiplier (PM) or aphoto-diode.
 3. An apparatus according to claims 1-2, characterised inthat said source (103) is comprised of or embedded in said moderator(104′).
 4. An apparatus according to claims 1-3, characterised in thatsaid source (103) is arranged essentially in proximity of or about/inthe centre of the face of said moderator (104′, 104″) that adjoins thelight-emitting unit (102 b).
 5. An apparatus according to claims 14,characterised in that said light-conductive unit (104′) is configuredessentially with a face that adjoins said light-emitting unit (102 b)and having a relatively smaller face adjoining a detection face (107) ofsaid light-registering unit (102 a).
 6. An apparatus according to claims1-5, characterised in that said light-conductive unit (104″) isconfigured for emitting light conducted from said light-emitting unit(102 b) to the light-registering unit (102 a) essentially perpendicularto a detection face (109) of the apparatus (100).
 7. An apparatusaccording to claims 1-5, characterised in that said light-conductiveunit (104″) is configured for emitting light conducted from saidlight-emitting unit (102 b) to the light-registering unit (102 a)essentially in parallel with a detection face (109) of the apparatus(100).
 8. An apparatus according to claims 1-7, characterised in thatthe apparatus further comprises an electric circuit (105) connected tosaid detector device (102; 102 a), wherein said circuit (105) isconfigured for generating a signal (108) that represents an estimatedamount of hydrogen, water and/or humidity content on the basis of theelectric signal (106) from said light-registering unit (102 a).
 9. Amethod of detecting the hydrogen content (101) of an object comprisingthe steps of: emitting fast/energy-rich neutrons from a neutron source(103); detecting thermal neutrons by means of a detector device (102;102 a; 102 b); braking and reflecting neutrons by collision of amoderator (104; 104′; 104″), characterised in that the method furthercomprises: emitting light by a light-emitting unit (102 b) in the eventof a nuclear event/reaction with a thermal neutron; emitting an electricpulse/an electric signal (106) by a light-registering unit (102 a) uponrecording of a flash of light; and conducting light from saidlight-emitting unit (102 b) to said light-registering unit (102 a) by alight-conductive unit arranged between said light-emitting unit (102 b)ands said light-registering unit (102 a); of which said moderator (104′;104″) is the light-conductive unit.
 10. A method according to claim 9,characterised in that said light-emitting unit (102 b) is a scintillatorand that said light-registering unit (102 a) is a photo-multiplier (PM)or a photo-diode.
 11. A method according to claims 9-10, characterisedin that said source (103) is comprised of or embedded in said moderator(104′).
 12. A method according to claims 9-11, characterised in thatsaid source (103) is arranged essentially in proximity of or around/inthe centre of the face of the moderator (104′, 104″) that adjoins thelight-emitting unit (102 b).
 13. A method according to claims 9-12,characterized in that said light-conductive unit (104′) is configuredessentially with a face that adjoins said light-emitting unit (102 b)and having a relatively smaller face adjoining a detection face (107) ofsaid light-registering unit (102 a).
 14. A method according to claims9-13, characterised in that said light-conductive unit (104″) isconfigured for emitting light conducted from said light-emitting unit(102 b) to the light-registering unit (102 a) essentially perpendicularto a detection face (109).
 15. A method according to claims 9-13,characterised in that said light-conductive unit (104″) is configuredfor emitting light conducted from said light-emitting unit (102 b) tothe light-registering unit (102 a) essentially in parallel with adetection face (109).
 16. A method according to claims 9-15,characterised in that the method further comprises generation, in anelectric circuit (105) connected to said detector device (102; 102 a),of a signal (108) representing an estimated amount of hydrogen, waterand/or humidity content, wherein said generation is performed on thebasis of the electric signal (106) from said light-registering unit (102a).